(1) Field of the Invention
The present invention relates to a new ventilation hood for tanks containing liquids which vent vapors, wherein the hood allows a variable amount of air to flow depending upon the work condition of the tank being vented. In particular, the present invention relates to a continuous ventilation system for tanks which release process fumes (vapors). The system demands low amounts of air for a particular ventilation hood for a tank when the tank is at rest and higher amounts of air when more fumes are being generated by the tank such as when workpieces are removed from the tank. The ventilation system is particularly adapted for an in line plating process.
(2) Prior Art
In recent years the electroplating industry and other users of industrial fluids have been paying increasing attention to the discharge of undesirable chemicals into the environment. Pollution by means of discharge of rinse water and air pollution by discharge of fumes or vapors from hot electroplating baths and toxic surface baths have become a major concern. The list of pollutants continues to grow based upon the EPA findings of new chemicals that are considered carcinogenic (cancer causing) materials. Loss of pollutants from a processing facility also has a direct bearing on economics of plant operation because the pollutants include chemical values, the loss of which must be made up by addition to the tank. The traditional way of handling the air pollution or ventilation of tank surfaces has been to incorporate hoods at the tank surface, a random length of duct and a fan. Not too many years ago this was considered an acceptable means of ventilating a facility.
In recent years, OSHA, the EPA and the DNR (Department of Natural Resources) have developed guidelines for indoor air quality, exhausted air quality and quantity of particulate or fume vapors being released from these processing facilities. Therefore, standards have been set which dictate air volume over a process to capture of vapors from the workpieces as they are removed from the bath. As a result, large amounts of air are constantly being exhausted from the facility, including the area above the process bath even when no parts being treated are being removed from the tank. These increased amounts of air require larger ducting, scrubbing devices and fans. The unseen items that go along with having this basically clean air being continuously exhausted is a larger air make-up unit to introduce fresh air to the facility to replenish the air being exhausted from the facility. Additional effluent is discharged to and must be treated by the waste treatment system. Higher electrical costs, higher maintenance costs and additional floor space are required to handle these larger systems that are removing air continuously from all the baths at both the tank surface and above the tank surface when there is a need to only continuously remove the air from the tank surface and periodically from above the tank surface.
There is a need to maintain total control over the tank surface with periodic and on demand above tank fixture ventilation, thus significantly decreasing the amount of air being exhausted from the facility on a continuous basis. This reduction in exhausted air will result in a significant reduction in the overall sizing and cost of the ventilation system. This would save the user thousands of dollars on the original purchase of the equipment, and also significantly reduce the overall operating costs of ventilating the process system. Thus, there would be reduced power consumption, treatment costs, air make-up requirements, including heating and cooling of the facility, and overall maintenance for an improved system.
The patent art has described ventilating systems of various types. Illustrative are U.S. Pat. No. 2,939,378 to Zalkind which shows a moveable or collapsible ventilation unit. U.S. Pat. No. 3,106,927 to Madwed shows a system with a closed top for a tank and doors which open and close to allow a workpiece into the closed top. The workpieces move down into the tank as a rail section is lowered on support columns. U.S. Pat. No. 3,205,810 to Rosenak shows an adjustable hood which covers a furnace mouth. U.S. Pat. No. 3,380,371 to Scheel describes a ventilation system for covering a pouring ladle using a flexible duct. U.S. Pat. No. 3,444,802 to Barton describes the use of vertical air curtains to seal off an area and to send fumes to an exhaust. U.S. Pat. No. 3,481,265 to Scheel describes a canopy or cover with a damper for regulating the venting from a ladle. U.S. Pat. No. 3,567,614 to Vauriac describes a shielded casing for workpiece handling which can be ventilated, thus recognizing the corrosive nature of plating fluids and the need for shielding. U.S. Pat. No. 4,087,333 to Naevestad describes a cover for a coke oven car which travels with the car. U.S. Pat. No. 4,150,605 to Telchuk et al describes a self-propelled spray booth for larger objects. U.S. Pat. No. 4,389,923 to Ludscheidt describes a moveable exhaust duct for automotive fumes and the like using an overhead system. U.S. Pat. No. 4,787,298 to Hon describes flexible exhaust ducts which are moveable.
U.S. Pat. No. 4,592,819 to Suzuki et al describes a high speed plating system where a single cover is used for exhausting accumulated gases from all of the tanks. The system is essentially closed except for the inlet and the outlet for the workpieces. U.S. Pat. No. 4,714,010 to Smart describes an exhaust ventilation system wherein an exhaust system is provided around the tank which is actuated when a reciprocating cover is opened. A hood is placed over the tank supporting the workpiece to be treated which is lowered into the tank. The tanks are vented as is the hood. The system is complicated and in use the moveable covers are not reliable. The system is also difficult to retrofit to existing plating tanks.
What is needed is an inexpensive, reliable system which can be retrofitted to existing systems, for regulating the amount of air flow through an exhaust system without sacrificing safety in exhausting gases from tanks containing liquids giving off fumes. Particularly included is a reliable system for plating.